1. Field of the Invention
The present invention relates to a high frequency sputtering device, and in particular to a high frequency sputtering device having a grounding shield which is arranged at the circumference of the target.
2. Description of Related Art
In the field of semiconductor devices, there is increasing integration and miniaturization of the elements. In order to respond to this, semiconductor manufacturing processes are carried out using high frequency sputtering devices for such operations as filling film inside minute holes. FIG. 10 is a sectional front view of a high frequency sputtering device. A circular cathode 14 is mounted at the mouth of the upper part of a processing chamber 10 by means of an insulator 12. An interface device 16, filter 18 and high frequency power supply 20 are connected in series with this cathode 14. A target 22 is mounted on the lower face of the cathode 14. A cylindrical grounding shield 24 is mounted on the processing chamber 10 in such a way that it surrounds the cathode 14 and the target 22. As shown in a magnified view in FIG. 11, the gap between the grounding shield 24 and the cathode 14 is narrow, being approximately 2 mm. The size of this gap is sufficiently smaller than the sheath thickness necessary to support plasma, in order to prevent ,plasma from entering the gap. The substrate holder 26 is arranged inside the processing chamber 10 so as to be opposite the target 22. A substrate 28 is mounted on this substrate holder 26.
The operation of this high frequency sputtering device will now be explained. Plasma is generated between the target 22 and the substrate 28 when the processing chamber 10 is exhausted by means of an exhaust device 32, electric discharge gas is introduced from a gas feeder in device 30 and high frequency electric power is applied to the cathode 14. Ions in this plasma are sputtered on to the target 22, particles of the target 22 are scattered, and these particles adhere to the surface of the substrate 28, so that a thin film is deposited on the surface of the substrate 28. The high frequency generally used in the high frequency power supply 20 is 13.56 MHZ.
In the conventional device in FIG. 10, because the gap between the grounding shield 24 on the one hand and the cathode 14 and target 22 on the other is narrow and long, large stray capacitances are generated in this gap part. The problem occurs that some of the high frequency electric current supplied from the high frequency power supply 20 flows into this stray capacitance and high frequency electric current is lost. This problem becomes particularly acute at high frequencies.
For this reason, a high frequency sputtering device in which the grounding shield is reticulate and the stray capacitance is small has been designed. See Japanese Patent No. 2832360. However, further problems arise with a reticulate grounding shield, such as the fact that its configuration is fragile and abnormal electric discharges are generated at the reticulate shield.
In addition, techniques are known in which the stray capacitance is reduced by laminating a plurality of metal plates on the rear surface of the electrode in order to reduce the loss of high frequency current in a CVD device (plasma CVD device) which uses plasma excited by high frequency waves. See Japanese Laid-Open Application No. S59-63775. However, this reference makes no mention of measures for reducing the stray capacitance when a grounding shield is provided at the circumference of the electrode. In the sputtering device there is the problem that, in order to prevent particles discharged from the target from adhering to the inner wall of the device, becoming detached, dropping down and forming particulates which contaminate the substrate, a grounding shield is provided in order to cover the end part of the target, and a large stray capacitance is generated between this grounding shield and the target. In the above-mentioned plasma CVD device, because only the stray capacitance of the rear face of the electrode is reduced, even if a sputtering device of such a configuration is used it is not possible to reduce the stray capacitance between the grounding shield and the target and the problem of the loss of high frequency current cannot be solved.